The floor Joist span chart and building code requirements are based on data from the 2012 International Residential Code using number 2 lumber.
Types of Floor Joists
Joists for use in residential framing applications fall into two different categories; tree sawed and engineered. This page focuses on the tree sawed variety. Kiln dried number 2 Pine is the most widely used material. It is relatively inexpensive and is widely available. It is available in sizes that will work for joists from 2 x 8 x 8′ to 2 x 12 x 24′. There are limits on how far these boards can span.
Floor Joist Span Chart for 40 lb Live Load
| O.C. | Type of Wood | 2×8 | 2×10 | 2×12 |
| 12″ | Southern Pine | 14’2″ | 18′ | 21’9″ |
| Hem-Fir | 13’2″ | 16’10” | 20’4″ | |
| Douglas Fir | 14’2″ | 17’9″ | 20’7″ | |
| Spruce-Pine-Fir | 13’6″ | 17’3″ | 20’7″ | |
| 16″ | Southern Pine | 12’10” | 16’1″ | 18’10” |
| Hem-Fir | 12′ | 15’2″ | 17’7″ | |
| Douglas Fir | 12’7″ | 15’5″ | 17’10” | |
| Spruce-Pine-Fir | 12’3″ | 15’5″ | 17’10” | |
| 19.2″ | Southern Pine | 12’1″ | 14’8″ | 17’2″ |
| Hem-Fir | 11’3″ | 13’10” | 16’10” | |
| Douglas Fir | 11’6″ | 14’1″ | 16’3″ | |
| Spruce-Pine-Fir | 11’6″ | 14’1″ | 16’3″ | |
| 24″ | Southern Pine | 11′ | 13’1″ | 15’5″ |
| Hem-Fir | 10’2″ | 12’5″ | 14’4″ | |
| Douglas Fir | 10’3″ | 12’7″ | 14’7″ | |
| Spruce-Pine-Fir | 10’3″ | 12’7″ | 14’7″ |
Floor Joist Span Chart for 30 lb Live Load
| O.C. | Type of Wood | 2×8 | 2×10 | 2×12 |
| 12″ | Southern Pine | 15’7″ | 19’10” | 24’2″ |
| Hem-Fir | 14’6″ | 18’6″ | 22’6″ | |
| Douglas Fir | 15’7″ | 19’10” | 23′ | |
| Spruce-Pine-Fir | 14’11” | 19′ | 23′ | |
| 16″ | Southern Pine | 14’2″ | 18′ | 21’1″ |
| Hem-Fir | 13’2″ | 16’10” | 19’8″ | |
| Douglas Fir | 14’1″ | 17’11” | 19’11” | |
| Spruce-Pine-Fir | 13’6″ | 17’2″ | 19’11” | |
| 19.2″ | Southern Pine | 13’4″ | 16’5″ | 19’3″ |
| Hem-Fir | 12’5″ | 15’6″ | 17’1″ | |
| Douglas Fir | 12’10” | 15’8″ | 18’3″ | |
| Spruce-Pine-Fir | 12’9″ | 15’8″ | 18’3″ | |
| 24″ | Southern Pine | 12’4″ | 14’8″ | 17’2″ |
| Hem-Fir | 11’4″ | 13’10” | 16’1″ | |
| Douglas Fir | 11’6″ | 14’1″ | 16’3″ | |
| Spruce-Pine-Fir | 11’6″ | 14’1″ | 16’3″ |
Floor Joist Building Code Requirements
The best way for a joist to transfer its load is for it to stack. This simply means for it to rest directly on top of another framing member like a drop girder, a wall, or a pressure treated mud sill. There is some criteria the joists must meet according o the 2012 International Residential Building Codes.
- The joist must have a minimum of 1 1/2″ riding on the wall or beam.
- If the joists are lapped, then they must be lapped at least 3″.
- Maximum end notches for 2 x 8, 2 x 10, and 2 x 12 respectively are 1 13/16″, 2 5/16″, and 2 13/16″.
- Use an approved hanger or a 2 x 2 ledger strip on flush beams for spans greater than 12′.
- When framing openings, use header and trimmer joists. Double any header over 4′ and any trimmer joists with a header attached within 3′ of its bearing.
- Use a minimum of 3 8d nails for toe nailing to girder or sill.
- Use a minimum of 3 10d nails for face nailing and lap joints.
Be aware that these spans and code requirements are taking things to the absolute limit. In a practical application it is a good rule of thumb to not use 2 x 8’s at all, never span a 2 x 10 over 14′, never span a 2 x 12 over 20′, and use as many nails as possible without damaging the wood.
